Field of the Invention
The present invention relates to a plugged honeycomb structure, and more particularly, it relates to a plugged honeycomb structure which is for use in an exhaust gas purifying device, a particulate trapping filter, or the like and includes plugging portions with which parts of cells are plugged.
Description of the Related Art
Heretofore, an exhaust gas emitted from an internal combustion engine such as a car engine includes toxic substances such as carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx). These toxic substances cannot be discharged to the atmosphere as they are because they have an influence on natural environments, human bodies and others. To eliminate such a problem, an exhaust gas purifying device (or a particulate trapping filter) to remove and purify the above toxic substances is usually disposed in the middle of emission through channels of the exhaust gas.
In the exhaust gas purifying device, for example, a honeycomb structure made of a porous ceramics material is used as a catalyst carrier, and in partition walls of the honeycomb structure, there is used a honeycomb catalyst body onto which an SCR catalyst or the like is loaded is used. Here, the honeycomb structure as the catalyst carrier includes the porous partition walls defining a plurality of cells extending from one end face to the other end face and formed as through channels for a fluid. Furthermore, plugging portions are formed to cells of the one end face in accordance with a predetermined arrangement standard, and the plugging portions are similarly formed to the residual cells of the other end face.
When the plugged honeycomb structure of the above constitution is used in the exhaust gas purifying device, the exhaust gas flows into the plugged honeycomb structure from the cells of the one end face in which the plugging portions are not disposed, passes through the partition walls and is finally emitted out from the cells of the other end face in which the plugging portions are not disposed. At this time, the exhaust gas passes through the porous partition walls, the partition walls therefore function as a filtering material, and particulates included in the exhaust gas are trapped in the partition walls and on the surfaces of the partition walls.
Consequently, it is possible to remove the particulates from the exhaust gas. Here, when the trapping of the particulates by the plugged honeycomb structure continues, and a lot of particulates are deposited on the surfaces of the partition walls, thereby obstructing pass-through properties of the exhaust gas. As a result, a difference in pressure is made between an inflow side of the exhaust gas (one end face side) and an outflow side (the other end face side), and so-called pressure loss is generated. In consequence, suitable pass-through of the exhaust gas is impaired and fuel efficiency (output) deteriorates.
Thus, the exhaust gas is treated as much as constant time or amount, and then there is performed a particulate removing treatment of, for example, injecting fuel to react the particulates deposited mainly on the surfaces of the partition walls with oxygen included in the atmosphere and gasifying the particulates into carbon dioxide to remove the particulates.
That is, in the exhaust gas purifying device in which the plugged honeycomb structure is used, a treatment of heating and removing the particulates deposited on the partition walls becomes essential, and in a case where an amount of the particulates to be deposited on the partition walls is large, frequency of the particulate removing treatment increases. As a result, the fuel efficiency might deteriorate. Additionally, when removing the particulates by the heating, it is difficult to gasify all the particulates deposited on the partition walls, and there is the possibility that parts of the particulates still remain as ash on the surfaces of the partition walls.
Furthermore, in the plugged honeycomb structure, parts of the cells of the one end face and the other end face are plugged, respectively, and hence there has been the large tendency that the pressure loss in an initial state prior to the treatment of the exhaust gas increases from the beginning as compared with a usual honeycomb structure.
Thus, as a plugged structure to remove the particulates included in the exhaust gas, there has been suggested a honeycomb structure in which it is possible to remove the particulates deposited on the partition walls and to decrease a residual amount of the ash after the particulates are removed, without requiring any special mechanisms, devices and others (see Patent Document 1).
Consequently, at least a part of a partition wall intersection region where the partition wall intersects the partition wall in a lattice-like manner includes “an intersection-less portion” in which the partition wall of a portion corresponding to the partition wall intersection region is not present. Thus, the intersection-less portion is disposed, and hence it is possible to inhibit the increase of pressure loss in a case where the plugged honeycomb structure is used in the exhaust gas purifying device or the like and it is possible to minimize the frequency of a particulate removing treatment by heating.
[Patent Document 1] JP-A-2004-132266